The present invention relates to isomeric mixtures containing greater than 50% cis-2-methyl-3-pentenoic acid produced by, interalia, a novel process and novel compositions using such mixtures of cis and trans isomers of 2-methyl-3-pentenoic acid to alter the flavor and/or aroma of consumable materials.
There has been considerable work performed related to substances which can be used to impart (or enhance) flavors to (or in) various consumable materials. These substances are used to diminish the use of natural materials, some of which may be in short supply and to provide more uniform properties in the finished product. Sweet, fruity, strawberry, winey-cognac, butter-like, rum-like, and butterscotch aromas as well as sweet, strawberry, nutty-coconut, fatty, butter-like, rum-like and butterscotch-like tastes are particularly desirable for many uses in foodstuff flavors. Green, sweet, sharp strawberry notes are desirable in perfume compositions. Notes having turkish-like characteristics as well as aromatic, sweet, bitter, woody and smokey notes are desirable in tobacco flavoring compositions.
U.S. Pat. No. 3,499,769 issued on Mar. 10, 1970 discloses processes for imparting a fresh fruity flavor (particularly strawberry flavor) to foods by adding a small amount of 2-methyl-2-pentenoic acid to the foodstuff. In U.S. Pat. No. 3,499,769 it is emphasized that the basic nuance imparted by 2-methyl-2-pentenoic acid is a "berry" flavor. Quite unexpectedly, the novel isomeric mixture of the instant invention has properties different in kind from the 2-methyl-2-pentenoic acid of U.S. Pat. No. 3,499,769 which is only fruity and strawberry-like and does not have the sweet, fruity, butter-like, rum-like and butterscotch aroma and taste qualities of the isomeric mixture of the instant invention. Other isomeric mixtures of 2-methyl-3-pentenoic acid are shown to be prepared by Boorman and Linstead, J.Chem.Soc. 1935, 258-67 (abstracted by Chem. Abstracts, Vol. 29, pages 2912 (7/8). 2-Ethyl-3-pentenoic acid is shown to be prepared by Fichter and Obladen, Berichte, 42, 4703-7 by distillation of alpha-ethyl gamma methyl paraconic acid which, in turn, is formed by reduction using a sodium-mercury amalgam of ethyl-alpha-ethyl aceto-succinate. The above-disclosed processes produce isomer mixtures which are considered to be different in kind insofar as their organoleptic properties are concerned from the isomer mixtures produced by the process of the instant invention.
Ethyl-2-methyl-3-pentenoate (95% 3:1 trans:cis isomer and 5% ethyl-2-methyl-2-pentenoate) has been offered as a development chemical by Toray Industries, Inc. of 2, Nihonbashi-Muromachi 2-chome, Chuo-Ku, Tokyo, Japan.
McGreer, et al, Can. J. Chem., 41, 726,31 (1963) discloses the production of various alkyl esters of pentenoic and butenoic acids by means of pyrolysis of 3,5-dimethyl-3-carbomethoxy .DELTA..sup.1 -pyrazoline. Thus, on page 728 of the McGreer article, products having the following structures are shown to be produced: ##SPC1##
Tsuji, et al, J.Am.Chem.Soc., 86, (20) 4350-3 (1964) discloses the production of alkyl alkenoates by means of reaction of carbon monoxide, alkenyl halides and alkanols with use of palladium chloride as a catalyst. Other methods for the synthesis of alkyl alkenoates are set forth in the following references:
i. French Pat. No. 1,389,856, issued Feb. 19, 1965; PA1 ii. Brewis and Hughes, Chem. Communications, (8), 157-8 (1965); PA1 iii. Bordenca and Marsico, Tetrahedron Letters (16), 1541-3 (1967); and PA1 iv. Hosaka and Tsuji, Tetrahedron, 27, (16) 3821-9 (1971). PA1 a. First preparing a 2-halo-3-pentene by intimately admixing hydrogen bromide with 1,3-pentadiene at a temperature of from -20.degree. up to +30.degree.C, preferably, from 0.degree. up to 10.degree.C and at a pressure, preferably, of atmospheric pressure. The 1,3-pentadiene (otherwise known as "piperylene" preferably has a purity of 90% but 50% piperylene may also be used. The 2-halo-3-pentene thus produced may be used in its crude form without further purification in subsequent reactions; PA1 b. The 2-halo-3-pentene is then reacted with magnesium to form a Grignard reagent, otherwise known as 2-magnesium halo-3-pentene. The reaction with the magnesium is carried out preferably in the presence of tetrahydrofuran, however, other solvents such as diethyl ether may also be used. The mole ratio of magnesium to halo-pentene is preferably from 1 up to 10 moles of magnesium per mole of halo-pentene. More preferably, from 3 up to 5 moles of magnesium per mole of halo-pentene. The temperature of reaction is from 10.degree. up to 50.degree.C; preferably from 10.degree. up to 20.degree.C. Temperatures lower than 10.degree.C gives rise to a reaction rate which is too slow to be economical. Temperatures higher than 50.degree.C give rise to side reactions causing an undue lowering of yield of product; PA1 c. The Grignard reagent produced in step (b) is then reacted with carbon dioxide (preferably in the form of crushed dry ice). The reaction with carbon dioxide may also be carried out by bubbling carbon dioxide into the Grignard reagent at atmospheric pressure at a temperature of between -20.degree. up to +40.degree.C, preferably from 0.degree. to 20.degree.C or reacting the Grignard reagent with gaseous carbon dioxide at higher pressures of from 10 up to 100 pounds per square inch absolute at temperatures up to 50.degree.C. When the reaction takes place with crushed dry ice, the temperature is the temperature of crushed dry ice. The carbonation forms magnesium halo salt of 2-methyl-3-pentenoic acid having the structure: ##EQU6## wherein X is halogen selected from the group consisting of chlorine and bromine; PA1 d. The last step in this process of the prior art involves the hydrolysis of the magnesium halo salt of 2-methyl-3-pentenoic acid in acid at a pH of from 2 up to 3. The preferred acid is a mineral acid such as hydrochloric acid or sulfuric acid. PA1 a. First preparing a methyl acetylene magnesium halide Grignard reagent by admixing, a methyl magnesium halide (the chloride, bromide or iodide) with a slight molar excess of methyl acetylene (preferably as "Mapp Gas", a commercial mixture of methyl acetylene and allene) at a temperature in the range of 40.degree.-60.degree.C (preferably 40.degree.-50.degree.C) in an inert solvent such as tetrahydrofuran or diethyl ether. Preferably, the reaction time range is from 4-12 hours; PA1 b. Preparing 3-pentyne-2-ol by first admixing the methyl magnesium halide reaction product preferably in its original reaction solvent with a slight molar excess of acetaldehyde to form a magnesium halo salt of 3-pentyne-2-ol, at a temperature in the range of 20.degree.-30.degree.C and then hydrolyzing the said magnesium halo salt of 3-pentyne-2-ol, preferably with a cold concentrated mineral acid such as concentrated hydrochloric acid in ice, and purifying the resulting 3-pentyne-2-ol using standard physical separation techniques, e.g., extraction and distillation; PA1 c. Preparing a 4-halo-2-pentyne (e.g., 4-chloro-2-pentyne or 4-bromo-2-pentyne) by means of halogenating the 3-pentyne- 2-ol with a slight molar excess halogenating agent, e.g., phosphorous trichloride, phosphorous tribromide, and SOCl.sub.2, at temperatures in the range of 20.degree.-80.degree.C, depending upon the halogenation reagent used. The preferred halogenating reagent is PCl.sub.3 using a temperature range of 20.degree.-25.degree.C; PA1 d. Preparing a 4-magnesium-halo-2-pentyne Grignard reagent by reaction of the 4-halo-2-pentyne with magnesium in a solvent, for example, tetrahydrofuran or diethyl ether at a temperature in the range of 25.degree.-50.degree.C, depending upon the solvent used; PA1 e. Preparing a magnesium halo carboxylate salt mixture of compounds having the structures: ##EQU7## (wherein X is halogen, e.g., chloro or bromo) by intimately admixing carbon dioxide (either in the gas phase, or as a solid in the form of powdered dry ice). The reaction with carbon dioxide may be carried out by bubbling carbon dioxide into the Grignard reagent at atmospheric pressure at a temperature of between -20.degree. up to +40.degree.C, preferably, from 0.degree. to 20.degree.C or reacting the Grignard reagent with gaseous carbon dioxide at higher pressures of from 10 up to 1000 pounds per square inch absolute at temperatures up to 50.degree.C. When the reaction takes place with crushed dry ice, the temperature is the temperature of crushed dry ice. PA1 f. Hydrolyzing the resulting magnesium halocarboxylate salt mixture with aqueous mineral acid (e.g., hydrochloric acid) at a temperature in the range of 20.degree.-30.degree.C to produce a crude mixture of: PA1 g. Preparing a mixture containing about 80% cis-2-methyl-3-pentenoic acid and 20% 2-methyl-2-pentenoic acid by hydrogenating the mixed acid product of step (f) supra in the presence of a palladium/CaSO.sub.4 catalyst containing 3% Pd preferably at a pressure in the range of 20-200 psig; preferably in a lower alkanol solvent such as methanol or ethanol at temperatures in the range of 20.degree.-40.degree.C, preferably 20.degree.-25.degree.C. The preferred weight percent range of catalyst is from 0.1 up to 1%. The resulting acid reaction product may then be purified using standard physical separation techniques, e.g., extraction and distillation. PA1 Geraniol PA1 Ethyl methyl phenyl glycidate PA1 Vanillin PA1 Ethyl pelargonate PA1 Isoamyl acetate PA1 Ethyl butyrate PA1 Naphthyl ethyl ether PA1 Ethyl acetate PA1 Isoamyl butyrate PA1 2-Methyl-2-pentenoic acid PA1 Elemecine (4-allyl-1,2,6-trimethoxy benzene) PA1 Isoelemecine (4-propenyl-1,2,6-trimethoxy benzene)
None of the above references sets forth a process for preparing the cis isomer of an alkyl pentenoic acid or mixtures containing more than 50% cis isomer.
Felkin, et al., Ann.Chem. (Paris) 6 (1), 17-26 (1971) discloses processes for producing "high cis" and "high trans" 2-methyl-3-pentenoic acid and methyl-2-methyl-3-pentenoate mixtures, according to the following reaction sequences: ##SPC2##
A process for preparing the "high cis" acid mixture is set forth in Felkin, et al, Chemical Communications, No. 802, pages 75 and 76 (Dec. 29, 1965).